(1) Field of the Invention
The present invention relates to a passive radar early warning system. More particularly the system eliminates spurious received signals and provides a unique audible signal of a frequency within the normal hearing range when the received signal is of a frequency outside the normal hearing range.
(2) Description of the Prior Art
There are several type prior art passive early warning receivers. One prior art system utilized summation of many RF bands following initial RF detection. This was followed by pulse stretching, additional amplification and an audio output. Due to difficulty in discerning between radar pulses and the summed noise the audio output warning of radar illumination suffered.
Another prior art passive early warning system reviewed each RF band separately for detection purposes. This helped reduce the problem of noise summation. However spurious signals and demodulated signals of a frequency outside the normal hearing range still provided a problem.